People who had a moderate intake of carbohydrates had the lowest risk of death from disease compared with those who ate a high- or low-carb diet. People who ate less than 30 percent of calories from carbs were predicted to have a life expectancy of 79 years; those who ate more than 65 percent of their calories from carbs had a life expectancy of 82 years; those who consumed 50 to 55 percent of their calories from carbs were estimated to have a life expectancy of 83 years.

How the Study Analyzed the Association Between Carb Intake and Lifespan

To reach their conclusions, the authors pulled data from the Atherosclerosis Risk in Communities (ARIC) study, which included more than 15,400 people ages 45 to 64. Participants completed a food frequency questionnaire at the start of the study and again six years later, reporting how often they consumed certain foods and drinks, as well as the serving sizes. Twenty-five years later, researchers analyzed their health information and determined who died. Next, researchers adjusted for factors including age, sex, race, total caloric intake, diabetes, cigarette smoking, physical activity, income, and education, and looked at the association between carbohydrate consumption and mortality.

On average, people ate 48.9 percent of their calories from carbohydrates. Overall, eating more animal protein and fat, and fewer carbs, was associated with a greater risk of death. But it wasn’t necessarily the amount but where these macronutrients were coming from. When people ate more plant-based proteins in the context of a low-carb diet, they were more likely to live longer.

"Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight-loss strategy,” Sara Seidelmann, MD, PhD, lead author and clinical and research fellow in cardiovascular medicine at Brigham and Women's Hospital in Boston, says in a press release. (The authors of the study declined to comment.) Dr. Seidelmann continued in the release, “our data suggests that animal-based low-carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall life span and should be discouraged. Instead, if one chooses to follow a low-carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy aging in the long term.”

What the Results Suggest About Popular Plans Like the Ketogenic Diet

Why did moderation win out? The authors speculated that low-carb diets may run high in animal-based proteins and low in veggies, fruits, and grains, which may cause someone to miss out on important phytochemicals, vitamins, and minerals that these foods supply. Skimping on plants and beefing up on meat may also increase disease-causing inflammation. On the other hand, high-carb diets may pack a greater amount of refined, high-glycemic carbs, which have a negative impact on metabolic health.

Today, the appeal of super-low-carb diets, like the ketogenic diet, or "keto" for short (or even "carnivore"), relies on the promise that people can eat an unlimited amount of animal foods (like fatty steak) and quickly lose weight. While many people have found slim-down success on these, the study suggests it may be to the detriment of their long-term health.

“Most people focus mainly on weight loss, when they should focus on healthy weight loss,” says Amy Stephens, RDN, CDE, a diabetes nutritionist in private practice in New York City. “Weight loss doesn’t always equal healthy,” she says. (Stephens wasn’t involved in the study.)

What to Take Away From the Findings if You’re Rethinking How You Eat Carbs

One limitation is that this is an observational study. Though food frequency questionnaires are often used in nutrition studies (and very good ones), they are notorious for potentially being inaccurate. It’s difficult for people to correctly remember what and how much they ate in the past.

“The best types of studies are large, randomized, double-blind, placebo-controlled trials that last a long time. In this article, they rely on data collected from many different research teams and analyzed the pooled data. This is not the best method of research,” says Stephens. But that doesn’t take away from their findings. “Although this may not be the best study design, the conclusion is something we have seen for a while in the medical community,” she says.

While headlines may scream that this study shows a low- or high-carb diet will kill you, the conclusion is more basic than that — and it’s far from new. “It’s time to get over your fear about eating nutrients. Eat healthy foods from all food groups, including carbohydrates,” says Lisa Young, PhD, RDN, an adjunct professor of nutrition at New York University and author of the forthcoming book Finally Full, Finally Slim. (Dr. Young also wasn’t involved in the study.) Dip too low in carb consumption, and you’ll miss out on fruits, vegetables, beans, and whole grains; eat too many carbs and you’re probably skimping on healthy fats, like avocado, nuts, and seeds.

How to Develop a Healthier Relationship With Carbs

Follow these guidelines for what you can do to eat well and still support a long life:

Revise your definition of “low carb.” Vegetarian sources of protein (including nuts, seeds, and beans) also contain a good amount of carbs, making it difficult to truly do a low-carb diet. And that alone may dissuade you from eating these nutrient-rich foods. Reducing carbs to 40 percent may be a more attainable approach.

Switch things up. When cutting carbs, stick to plant-based fats and proteins. In the study, people following an animal-based low-carb diet ate more beef, pork, lamb, chicken (with and without skin), and cheese. But the plant-based low-carb diet included more nuts, peanut butter, bread, and chocolate compared with high-carb diets. (Yes, people still managed to fit in bread.)

Make smart choices. “Pick the healthiest options from the different nutrient categories,” says Young. For instance, chickpeas are a nutrient-dense source of carbohydrates, while pretzels are not. Both are carbs and are equally maligned on trendy low-carb diets. Unless you’re allergic, there’s no reason to fear a chickpea.

Consider medical conditions. As a diabetes educator, Stephens, for one, promotes a plant-based diet to treat and prevent type 2 diabetes. She says very-low-carb diets are damaging for these patients. “In my practice, I work with many patients that have prediabetes and diabetes, and I have not seen any successful cases that follow a very low carb diet. In fact, I’ve seen worsened blood sugars and increased weight from them,” she says.

If you’re still committed to low-carb, know the risks. Sticking with an animal-based low-carb diet? Keep in mind that you’ll be missing out on certain nutrients, says Stephens, so you may need supplements, like fiber, potassium, and folic acid. Always talk to your doctor or a registered dietitian before embarking on a dietary change.